Various materials have been incorporated in organopolysiloxane compositions to improve the thermal conductivity of the resultant elastomers. For example, U.S. Pat. No. 3,499,859 to Matherly discloses adding boron nitride particles to room temperature vulcanizable organopolysiloxane compositions to form thermally conductive silicone elastomers. Also, U.S. Pat. No. 4,292,225 to Theodore et al, describes highly filled organopolysiloxane compositions containing boron refractory powders having good thermal conductive properties.
In contrast to the teachings of U.S. Pat. Nos. 3,499,859 and 4,292,225, it has been found that organopolysiloxane compositions having increased filler loadings provide elastomers having desirable physical properties as well as excellent thermal conductivity. Moreover, the compositions of this invention are useful for insulating electrical components because they permit any heat which is generated to be conducted away from the electrical component. Furthermore, the compositions of this invention are unique in that filler loadings in excess of 60 percent by weight based on the weight of the composition can be achieved using silicon nitride particles and the resultant elastomers have superior thermal conductivity and desirable physical properties.
It is, therefore, an object of this invention to provide a highly filled thermally conductive vulcanizable organopolysiloxane composition containing silicon nitride particles. Another object of this invention is to provide a thermally conductive composition having unique physical properties by virtue of the use of silicon nitride particles in filler loadings in excess of 60 percent by weight based on the weight of the composition. Still another object of this composition is to provide a highly filled composition which is sufficiently pliable that it can be extruded and cured. A further object of this invention is to provide highly filled heat curable compositions having improved thermal conductivity.